Metal sweating process



Jan. 10, 1961 s. A. GLUECK 2,967,769

' METAL SWEATING PROCESS Filed April 29, 1958 sewer? RECOVERED 0 l 2 3 4 5 G 7 8 7 ll I2 I3 l4 l5 l6 l7 l8 I9 2/ 22 24 25 2 27 Zn C1 INVENTOR.

3QMUEL H. GLUECK .BYML aw United States Patent METAL SWEATING PROCESS Samuel A. Glueck, Chicago, Ill., assignor to American Smelting and Refining Company, New York, N.Y., a corporation of New Jersey Filed Apr. 29, 1958, Ser. No. 731,756

1 Claim. (Cl. 75-78) This invention relates to a method of sweating metal comprised of lead from less fusible material with which the leady metal is physically associated. More particularly, it relates to a method of sweating a leady metal from less fusible metal, and especially to sweating solder from copper and copper-base alloys.

In one aspect, the invention comprehends immersing and agitating such material in a molten salt bath comprised of inert chloride salts and containing zinc chloride as an activating agent while maintaining the temperature of the bath below about 1000 F., thereby melting lead-comprising metal away from the less fusible material, and recovering the thus separated leady metal from the bath.

An advantage of the invention is that it provides an efficient and economical sweating procedure. Another advantage, especially in sweating leady metal from copper or copper-base alloys, is that loss of the latter metal by oxidation is reduced or avoided. Another important advantage is that, because of the temperature involved, the process can be conducted in a steel or cast iron kettle. These and other advantages will become apparent from the following more detailed description of the invention.

In general, the material contemplated for treatment by the invention is metal scrap or waste material of the type collected for processing in the secondary metal industry and comprises lead or lead-base alloys phys cally mixed with or attached to less fusible material. Thus, for example but not by way of limitation, the following materials may be treated in accordance with the process to recover leady metal therefrom: discarded automobile radiators to sweat from the surfaces of the radiators lead-tin solder which was used to solder together the various copper or brass elements of the radiator; Babbitt lined bearings to sweat the lead-tin Babbitt metal from the brass backings of the bearings; electro-type plates such as copper, magnesium, or aluminum and 2,967,769 Patented Jan. 10, 1961 grade drosses, the principal or major constituent of the leady metal may be tin.

Any chloride salt or salts which are inert, i.e. which are without, or substantially without, fiuxing action with respect to the material to be treated, may be used as the inert chloride salts in thetmolten bath in amounts to provide a bath having a melting point below 1000 F. and preferably in the range 750 to 900 F. Thus, in addition to the zinc chloride, the bath may contain various amounts of inert chlorides such as sodium chloride,

potassium chloride, magnesium chloride, strontium chloride, barium chloride, etc., to provide a bath having a melting point below 1000 F.

For best results, magnesium chloride and sodium chloride are used as the inert chloride salts of the bath and a molten bath is established which comprises, by weight, 38 to 63% magnesium chloride, 30 to 53% sodium chloride, and 3 to 15% zinc chloride. The most preferred composition within this range is one in which the ratio of the magnesium chloride to the sodium chloride corresponds to, or closely corresponds to, the eutectic composition of the MgCl -NaCl binary system, which eutectic occurs at about 56%, by weight, of magnesium chloride and 44%, by weight, of sodium chloride. Thus, preferably a molten pool is established which comprises, by weight, about 47 to 54% magnesium chloride, 38 to 43% sodium chloride and 3 to 15% zinc chloride. Also for best results, the temperature of the molten pool is maintained in the range 900 to 1000 F. during the sweating step. Agitation during the sweating step is necessary to shake the molten leady metal from the less fusible material and may be obtained either or both by agitating the pool or by agitating the material immersed in the pool. For best results, at least the latter is employed.

plastic-backed electrotype plates to sweat the lead-tinantimony electrotype metal from the backing of the plates; irony white metal turnings to sweat from the steel turnings the lead-tin alloys present thereon; soldered gas meter boxes to sweat the lead-tin solder from the steel body of the boxes; discarded lead-sheathed electrical cable to sweat the lead from the copper Wire in the cable; mixtures of lead, tin and aluminum foil to sweat the lead and tin from the aluminum in the mixtures; and various lead-tin drosses, i.e. mixtures of metal particles mixed with oxides thereof, to sweat the metal from the mixtures, for example solder or Babbitt drosses, or high grade tin drosses in which the metal particles are largely composed of tin. In the foregoing examples the lead-comprising metal in the material to be treated typically possesses a melting point below 750 F. while the less fusible metal or oxides or other inorganic material melts above 1000 F. Also, the principal or major constituent in the metal sweated from the mixture to be treated, typically, is lead although in some of the materials, for example in some Babbitt bearings and high The process is based on the discovery, contrary to expectations, that the addition of zinc chloride, whch is a powerful fiuxing agent, to the molten inert chloride salts, has an important and critical effect upon the efficiency of the process in that the zinc chloride enhances rather than decreases the amount of leady metal swea ed from the less fusible material. The effect of zinc chloride is shown by the following examples. It should be understood, however, that the examples are given for purposes of illustration and that the invention in. its.

broader aspects is not limited thereto.

In each of the examples tabulated in Table I a salt mixture containing, by weight, 56% MgCl and 44% NaCl was melted in a crucible in a pot furnace. Zinc chloride in the amounts set forth in Table I was then added to each bath. Weighed amounts of honeycomb radiator cores from discarded automobile radiators were treated in each bath to sweat leady metal therefrom. The honeycomb cores were of conventional construction and were composed of copper elements soldered together with lead-tin solder.

In each example, the weighed amounts of honeycomb cores were placed in an open-mesh basket which was then immersed in the molten salt bath for the time indicated in Table I to sweat solder from the cores. During the immersion period the temperature of the molten bath in each case was maintained at 970 F.' -15 F. and agitation was obtained by shaking the basket with an up and down motion and by stirring the molten salt. In sweating from the core, the solder became molten and dropped into the salt bath; however, the copper elements of the core did not melt and remained in the basket- At the end of the immersion period, the basket was removed from the molten bath. After the molten salt had drained from the basket, the copper elements in the latter were removed therefrom and were washed in running water and then dried and weighed. The molten salt bath was then carefully decanted until a small amount of salts and the solder remained in the crucible; Theresidue was then emptied into another container. The

Immersion Time and Percent Solder Percent by Recovery Example weight ZnClI in the bath Mins. 7 Mins:

25% Zn Oh The results set forth in Table I are shown graphically in the single figure of the accompanying drawing in which percent solder recovered versus percent ZnCl in the molten pool is plotted. In. the. drawing, curve A is a plot ofthe amount of solder removed .with. varying per:

centagesof zinc chloridein the bath, using a. five-minute.

immersion period. Curves B, C and D are similar plots in which immersion timeof.7, and 3 minutesrespeth tively were used.

It will be seen from these data and the shape of curves A, B and C, that the solder recovery increased steeply as the amount of zinc chloride in the bath was increased to 3%. With increasing amounts of Zinc chloride above. 3% in the bath, the solder recovery continued to increase at a steep; but lower rate reaching a maximum at about 10% zinc chloride in the bath. Thereafter, as the amount of zinc chloride was further increased, the solder recovery decreased comparatively rapidly as the amount of zinc chloride in the bath wasincreased to about With increasing amounts of zinc creased at a steady low rate. Accordingly, it will be seen that the presence of zinc chloride in the molten pool is critically important because ofitsenhancing effect on solder recovery; and, that the addition of about 3 to 15% zinc chloride to the bath is critically important to the amount of solder recovered.

It will also be observed from the data given in Table I and the curves of the drawing, that the amount of solder recovered with the three-minute immersion period was consistently lower than that recovered, with, the longer, immersion periods. at the higher concentrations of zinc'chloride in the bath,

the amount of solder recovered decreasedas the'rimrnerimmersion periods in excess of about three minutes are.

used. Preferably, the immersion period is about fiveto ten minutes in duration.

Example 7 The basket dipping procedure described for Examples 1 through 6 was used to treat antimonial lead inserts which were molded into hard rubber storage battery cell covers to sweat the antimonial lead-therefrom. A salt mixture containing, by weight,.55% magnesiumchloride I It will be noted .furtherthat,

and 45% sodium chloride was melted in a steel kettle, after which zinc chloride amounting to 10%, by weight, of the mixture was added to thekettle and was melted into the mixture. The basket containing the inserts was immersed in the molten pool for a period of eight minutes while maintaining the bath. atia temperature of 900 F. Also during the immersion period the bath was stirred with a motor-driven stirrer. A- clean separation and recovery of the antimonial lead metal from the charged material was obtained.

Example 8 The procedure of Example 7 was repeated to sweat the Babbitt metal from discarded Babbitt-lined brassbearing plates, using a salt bath of the same composition as that of Example 7 but with an immersion period of ten minutes and a bath temperature of 950 F. The Babbitt metal was completely separated from the backing plates which remained in the basket. Babbitt metal amounting to 7.5%, by weight, of the material charged to the baskets was recovered from the molten salt bath.

Example 9 The procedure of Example 8 was repeated using the same salt bath composition, bath temperature and immersion time to sweat the type metal from discarded copper backed electrotype plates; Type metal amounting'to 96.8%, by weight, of the charge was recovered and no dross was formed. These results are to be compared with those obtained in the conventional procedure in' which'the electrotype plates are sweated on the hearth of a conventional sweating furnace. In a test of the conventional procedure, type metal amounting to 88%, by weight, of the charge was recovered and dross amounting to 2%, by weight, of the charge was produced. Such results are typical of those obtained by the conventional procedure.

Example 10 metal physically associated with less fusible metal having amelting point above 1000 F. to remove the leady metal therefrom by sweating without melting the less fusible. metal which comprises immersing and agitating said scrap for a period of time of about five to ten minutes in amolten salt bath containing 38 to 63% magnesium chloride; 30 to 53% sodium chloride and 3ito' 15% zinc chloride-while maintainingthetempera ture of the bath below about 1000 F. thereby melting the leady metal and shaking the same from the less fusiblemetal without melting the latter metal whereby the leady metal is separated from the less fusible metal and is. physically incorporated into said salt bath, and separately recovering the thus separated leady metaland the lessfusible metal from the salt bath.

References'Clted in the file of this patent UNITED I STATES PATENTS 1,395,820 Harris Nov. 1, 1921 1,939,667 Csanyi Dec. 19, 1933 1,960,239.: Callis etal. May 29, 1934 

